[Help-bash] ${var//!([[:class:]])} removing characters of the [:class:]

[Mart Frauenlob]

Hello,

am I wrong if I think that an extglob pattern of i.e. !([[:digit:]]) 
should match all non-digit characters? Why don't they match in the 
example below? Why are non-digit chars removed?

# cat extg
#!/bin/bash

shopt -s extglob

echo "address@hidden"

x=".:3:."

echo "Y${x}"
echo remove digits
echo "Y${x//@([[:digit:]])}"
echo remove non-digits
echo "Y${x//!([[:digit:]])}"
echo remove punct
echo "Y${x//+([[:punct:]])}"
echo remove non-punct
echo "Y${x//!([[:punct:]])}"

# /opt/bash42/bin/bash extg
4.2.42(1)-release
Y.:3:.
remove digits
Y.::.
remove non-digits
Y
remove punct
Y3
remove non-punct
Y


Best regards

Mart